Voltage Drop -- Slowdown of motors


My team is using three motors, and several other things on the robot, and we are afraid that after the battery is drained, or down to a certain voltage that we won’t be able to keep our shooter wheel going at a constant speed for us to shoot.

Now, my mentor suggested we crank up the PWM’s more as the current drops by having a geartooth sensor check the speed of the wheel, and once it drops we crank the PWM’s.

Will this work? Or will we accomplish nothing, and once the battery is drained it is basically a lost cause anyways, and it is not needed anymore at all.

what your mentor is describing is a closed loop feedback system

yes it will work, the caveat is your max wheel speed will have to be something less than the full speed of the motor.

When the battery is fully charged the PWM values might be 200. Then as the battery gets lower the PWM values will go up, 210, 220…to 254, whatever it takes to keep the wheel spinning at the ‘right’ speed.

At that point you feedback system will be ‘railed’ and wont be able to keep up.

Its a great idea: it will hold the wheel speed constant as long as the battery is able to supply the power needed.

BTW, a bonus of this system, when you launch a ball the sensor will see that the wheel has slowed down, and it will increase the PWM output to get it back up to launch speed. This means you will be able to fire sequential shots faster.

Feedback is one of the most powerful tools an engineer has at his disposal!

EDIT: and the spell check is the 2nd most powerful tool (edited for speeling :^)

Thank you very much for the information.